1. Field of the Invention
The present invention relates to an electro luminescent element and in particular to improved organic compound materials for use in an electro luminescent element.
2. Description of the Related Art
An electro luminescent element is constructed by layering, in order, a transparent first electrode (such as, for example, an ITO), an organic compound layer with an organic compound having strong fluorescence, and a second electrode formed of a metal (such as, for example, Mg). The organic compound layer is constructed by layering a hole transporting molecule, a luminescence molecule, and an electron transporting molecule in order, and emits light when electric field is applied between the pair of electrodes. In other words, when holes are injected from the first electrode and electrons are injected from the second electrode, the injected holes and electrons move through the organic compound layer and collide with each other to recombine and vanish. By this recombination, energy is generated which is then used to produce an excited state of the luminescence molecule so that the element emits fluorescent light.
Such an electro luminescent element has advantageous characteristics over other display elements such as a liquid crystal, a plasma display, or an inorganic electro luminescent element, such as no limitation on the angle of view, capability of being driven at a low voltage, and rapid response.
As a hole transporting material of the organic electro luminescent element, a TPD (tetraphenylbenzidin) which has been proposed by Tang et al. is widely in use. Because TPD has superior hole transporting ability, an organic electro luminescent element using TPD as a hole transporting molecule such as, for example, an element having a structure, [ITO/TPD (60 nm)/Alq3 (60 nm)/Mg:Ag (1500 nm)], has an excellent initial performance with a maximum luminance reaching few tens of thousand cd/m2.
PBD (t-butylbiphenylylphenyloxadiazole) has been proposed as an electron transporting material by Tsutsui et al. PBD is a material having a high electron transporting ability and, at the same time, is a blue luminescence material of high luminance.
However, even though each of the conventional hole transporting, luminescence, and electron transporting molecules have good electric functionality characteristics, they also suffer problems of high crystallinity and low heat endurance. Because of these disadvantages, most of these materials cannot be used as materials for an organic electro luminescent element. For example, even though TPD (tetraphenylbenzidin) and triphenylamine are materials with good hole transporting ability, they exhibit high crystallinity and low heat endurance, which causes crystallization leading to element breakdown within one month after forming an element.
Similarly, even though PBD (t-butylbiphenylylphenyloxadiazole) is a material with good electron transporting ability, it has a fast crystallization, leading to an element breakdown within one week of forming a film.
The present invention is conceived to solve the above problems and an object of the present invention is to provide an electro luminescent element using functional molecules each having a function of hole transporting ability, luminescence, and electron transporting ability, the electro luminescent element having high heat endurance and low crystallinity.
According to one aspect of the present invention, in order to achieve the above object, there is provided an electro luminescent element comprising one or more organic compound layers between the electrodes, wherein at least one of the organic compound layers is a condensed ring compound derivative represented by a chemical formula, 
in which A1 and A2 represent substituents, B1 through B6 represent directly combined or 2 functional substituents, and R1 and R2 represent functional units such as triphenylamine, coumarin, and oxadiazole derivative, etc., with each of the functions of hole transporting ability, luminescence, and electron transporting ability.
With the structure defined above, by using a condensed ring compound derivative for each of the functional molecules of hole transport, luminescence, and electron transport, low crystallinity and high heat endurance which are preferable characteristics of an organic electro luminescent element can be added while maintaining good electric characteristics. This is because the condensed ring compound has a non-planer structure and reduced symmetry of the molecule shape. Because of these factors, the crystallinity of the molecule is reduced and the movability of the molecule can be reduced by introducing a molecular skeleton of a rigid condensed ring compound, resulting in improved heat endurance.
According to a second aspect of the present invention, there is provided an electro luminescent element with the structure of the first aspect, wherein each of the functional units R1 and R2 is selected from the group consisting of triphenylamine, coumarin, and oxadiazole derivative.
According to a third aspect of the present invention, there is provided an electro luminescent element with the structure of the first aspect, wherein the condensed ring compound derivative is distributed among host materials and the host material is further layered in the organic compound layer.
According to a fourth aspect of the present invention, there is provided an electro luminescent element with the structure of the first aspect, wherein the condensed ring compound derivative has a structure represented by one of the following chemical formulae (a)xcx9c(1): 
in which R represents the functional units.
According to a fifth aspect of the present invention, there is provided an electro luminescent element with the structure of the first aspect, wherein the functional unit has a structure represented by one of the following chemical formulae (r1)xcx9c(r22): 
in which n, m, and i represent integers, R represents saturated hydrocarbon from C1 through C30, an isomer thereof, or an aromatic compound.
According to a sixth aspect of the present invention, there is provided an electroluminescent element with the structure of the fifth aspect, wherein R is aromatic and is selected from the group consisting of phenyl, naphthyl, indenyl, fluorenyl, phenanthryl, anthranyl, pyrenyl, chrysenyl, naphthacenyl, benzophenanthrenyl, furanyl, thiophenyl, pyrrolyl, oxazolyl, isoxazolyl, pyrazolyl, triazolyl, furazanyl, pyridyl, oxazyl, morpholyl, thiazyl, pyridazyl, pyrimidyl, pyrazyl, triazyl, benzofuryl, isobenzofuryl, benzothiophenyl, indolyl, isoindolyl, benzoxazolyl, benzothiazolyl, benzoimidazolyl, chromenyl, quinolyl, isoquinolyl, cinnolyl, phthalazyl, quinazolyl, quinoxalyl, dibenzofuril, carbazolyl, xanthenyl, acridinyl, phenanthridinyl, phenanthryl, phenazinyl, phenoxazinyl, thianthrenyl, indolizinyl, quinolizinyl, naphthyridinyl, purinyl, oxadiazolyl, and oxathiazolyl.
According to a seventh aspect of the present invention, there is provided an electro luminescent element comprising one or more organic compound layers between the electrodes, wherein at least one of the organic compound layers is an adamantane derivative represented by the following chemical formula, 
in which R1 through R8 represent substituents, and Ar1 and Ar2 represent functional units having hole transporting ability, luminescence, and electron transporting ability.
According to the structure mentioned above, the organic compound layer is a compound having the adamantane derivative as its main skeleton and the adamantane derivative is a rigid molecule with a good heat endurance. By introducing substituents on R1 through R8, rotation around the connecting axes between the adamantane and benzene ring and between the benzene ring and the substituent unit are constrained, so that the movability and internal rotation of the molecule is reduced, resulting in improved heat endurance compared to a case without substituents.
According to an eighth aspect of the present invention, there is provided an electro luminescent element with the structure of the seventh aspect, wherein the adamantane derivative is distributed among host materials and the host material is further layered in the organic compound layers.
According to a ninth aspect of the present invention, there is provided an electro luminescent element with the structure of the seventh aspect, wherein the substituents R1 through R8 are substituted with a functional group including alkyl group, aryl group, allyl group, alkene group, alkyne group, alkoxy group, hydroxyl group, hydroxylate group, thiocarboxy group, dithiocarboxy group, sulfo group, sulfino group, sulfeno group, oxycarbonyl group, haloformyl group, carbamoyl group, hydrazinocarbonyl group, amidino group, cyano group, isocyano group, cyanato group, isocyanato group, thiocyanato group, isothiocyanato group, formyl group, oxo group, thioformyl group, thioxo group, mercapto group, amino group, imino group, hydrazino group, aryloxy group, sulfide group, halogen group, nitro group, and silyl group.
According to a tenth aspect of the present invention, there is provided an electro luminescent element with the structure of the seventh aspect, wherein each of the functional units Ar1 and Ar2 has an aryl skeleton as a basic skeleton.
According to an eleventh aspect of the present invention, there is provided an electro luminescent element with the structure of the tenth aspect, wherein the aryl skeleton is selected from the group consisting of phenyl, naphthyl, and phenanthryl.
According to a twelfth aspect of the present invention, there is provided an electro luminescent element with the structure of the tenth aspect, wherein the functional units Ar1 and Ar2 is further substituted by functional groups including alkyl group, aryl group, allyl group, alkene group, alkyne group, alkoxy group, hydroxyl group, hydroxylate group, thiocarboxy group, dithiocarboxy group, sulfo group, sulfino group, sulfeno group, oxycarbonyl group, haloformyl group, carbamoyl group, hydrazinocarbonyl group, amidino group, cyano group, isocyano group, cyanato group, isocyanato group, thiocyanato group, isothiocyanato group, formyl group, oxo group, thioformyl group, thioxo group, mercapto group, amino group, imino group, hydrazino group, aryloxy group, sulfide group, halogen group, nitro group, and silyl group.
According to a thirteenth aspect of the present invention, there is provided an electro luminescent element with the structure of the seventh aspect, wherein the derivative has a structure represented by the following formulae, (a1) to (a11) and a(13). Alternatively, the derivative may have the following norbornane structure, (a12). 